- The first episode, "33", where the Cylons relentlessly appear and attack every 33 minutes - pure 200 proof nightmare fuel.
- The whole miniseries. What started out as a normal day in Colonial life, falls apart extremely rapidly as the Cylons attack and utterly decimate the Colonies. Ships filled with passengers, cargo transports, mining ships are all left stranded as the Colonies fall. The whole atmosphere is one of dread and horror as the reality of what is happening sets in for everyone who survived. It evokes the horror of 9/11 very well; the same uncertainty, lack of information and chaos is present.
- President Roslin has assembled a fleet of over 60 civilian ships, stranded in space lanes when the Colonies came under attack. The makeshift fleet is in formation and plans are in motion to transfer passengers off the non-FTL capable ships, when suddenly a Raider jumps in, scans them and jumps away. Faced with an imminent Cylon attack, President Roslin makes the gut-wrenching decision to have all FTL capable ships jump away, abandoning the sublight only ships. The pleading cries of the ship captains being left behind are absolutely horrific to hear. Imagine being on one of those ships, unable to escape, watching others jump away, and then four Raiders jump in...
- Gaius having a nightmarish vision of Adama drowning his metaphorical daughter.
- The Cylon attack on the colonies in the original miniseries bothered me to no end. I think it might have been the orbital view of the mushroom clouds silently bursting over the whole planet, knowing that everyone you knew who wasn't right there with you is now dead. Similarly, the scene where the vipers go dead during a cylon attack and the pilots are trapped in hunks of metal, dead in space, helpless, waiting to be killed.
- The depiction of what was going on planetside in the feature length episode The Plan was pretty grim too. Highlights include a montage of various Colonies (some of which we had never seen before) being depicted as burning ruins, Tory and Ellen Tigh being hit by the blast wave, the Centurions roaming the streets killing survivors and, for extra nightmare fuel, charred corpses of those too close to the blasts. The whole holocaust in general qualifies as HONF, and plays upon the (quite rational) fear of nuclear war.
- The look of absolute cold fury on Adama's face when Starbuck confesses her role in Zak's death. Katee Sackhoff has said you're not seeing acting from her in that scene; she was genuinely terrified that he was about to beat her up.
- The Centurions boarding Galactica in "Valley of Darkness", particularly the very first time the characters run into one. Flyboy, Kat and Apollo are walking merrily through a darkened corridor, unaware of any problems beside the loss of power, when suddenly Kat screams, and Flyboy runs right into a seven foot steel monster. The thing flexes its hand briefly before tearing through Flyboy's chest with its metal claws (spraying Apollo with blood in the process), and then swatting him aside before he can even finish bleeding to death.
- The Pegasus approach to interrogating Cylons, be it the tortured, raped and Driven to Suicide Number Six Gina, or especially the scene in which officers from the Pegasus attempt to rape an unsuspecting and pregnant Sharon Agathon.
- The moment Admiral Cain Jumped Off The Slippery Slope. Badly outnumbered during a Cylon attack she orders her XO, Colonel Belzen to launch the Viper wing held in reserve. Belzen, a loyal officer who has known her for years, objects because he knows it's a Suicide Mission and their only chance is to retreat. Cain orders him to hand over his sidearm as if she is relieving him of duty. Instead, when he gives it to her she shoots him right between the eyes in the middle of the CIC. Cain then calls for the next officer in line (Colonel Fisk), tells him that he is the new XO and repeats her order to launch Vipers.
- New Caprica. ALL OF IT! Although the end of the arc has heavy doses of awesomeness. During some of the parts with Kara, if you listen very carefully to seconds without music or dialogue, you can hear people screaming.
- Special mention to the scenes of Kara being imprisoned by Leoben. She's stuck living with what essentially is her stalker, who's stronger than her, a religious nut who goes on about how God's plan involves them being together, and no matter how many times she kills him, he just keeps coming back.
- The Body Horror segments of the new Battlestar Galactica movie Razor are not as disturbing as the Hybrid, especially compared to the Minority Report hybrids already seen: an old man, responsible for the aforementioned Body Horror, talking cryptically and accurately about events still to come, about a main character being the root of everyone's doom, all while sitting in a tub of goo with cables going in and out, and finally reminding us, "All of this has happened before, all this will happen again. Again. Again. Again. Again," before calmly dying.
- From the Razor Flashbacks, the destruction of Columbia, specifically the screaming of her crew over the radio after the ship has already exploded, until it finally cuts out.
- In the finale, the look on Tyrol's face when he finds out what happened to Cally. He's thoughtful, working through it, then you see his nostrils flare and he just goes O_o and promptly breaks Tory's neck. Remember, this is one of the nicest, friendliest characters in the series.
- Leoben Conoy snapping his chains and turning over a steel table like it was nothing before attacking Starbuck. If You look closely, there's a brief moment after he breaks his cuffs that the battle-hardened Starbuck, who has been laughing at him the whole time, jumps back and starts looking genuinely terrified.
- Dualla's sudden, shocking and violent suicide after pretending to be happy will leave a mark on even the most well-adjusted.
- In season 4.0, even though she was The Scrappy, Cally's death by airlock (in front of her son no less) is absolutely chilling. Even worse, before Tory showed up, there was every indication that Cally planned to throw herself out the airlock, along with the aforementioned infant son. Let's repeat: a baby, being subjected to all the horrible things empty space does to you before killing you. Thankfully, the writers didn't take it that far; just dangling the possibility was horrifying enough.
- Being informed you and everyone like you will be boxed indefinitely.
- Finding out you're a Cylon sleeper agent.
- If you're even accused, possibly even tried for treason, good frakking luck.
- A humorous In-Universe example occurs when Baltar sees Head Baltar and is clearly only restrained from wigging out by remembering he's in public.
- Athena's shooting dead one of the Sixes out of a mistaken belief that she intends to kidnap Hera. Not only is it unnerving how she screams at the Six and threatens to shoot her (and even Tigh when he orders her to stand down) if she so much moves a muscle, but the way that she puts another bullet in the already mortally-wounded Six while she's on the ground just takes things from what could at least be construed as an act of panic into an outright execution. And the kicker? When Adama gives Athena a What the Hell, Hero? speech at the start of the following episode, she's completely unrepentant at having effectively murdered an innocent woman for absolutely no reason, only showing remorse at the possibility that she may have jeopardized the fledgeling alliance between the colonials and rebel Cylons, and then looking about ready to kill Adama with her bare hands when he orders her thrown in the brig, with no access to Hera.
Nightmare Fuel / Battlestar Galactica (2003)